Telephone system



Jan. 3, 1933. T. F. CROCKER TELEPHONE SYSTEM Filed Marsh 2, 1952 T 0% TWW InTJEfiIEF Thomas F Cracker" Patented Jan. 3, 1933 entree STATES PAT NT castes THOMAS F. CROCKER, OF CHICAGO, ILLINOIS, ASSIGNOR TO ASSOCIATED ELECTRIC LABORATORIES, INC OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE rnn'nrnonn SYSTEM Application filed March 2, 1932. Serial No. 596,303.

The present invention relates in general to telephone systems, but is concerned more particularly with small automatic exchanges, commonly known as private automatic ex changes, of the type employing an attendants cabinet for completing calls to and from distant exchanges. The main object of the invention is to provide an arrangement for giving secret service to a limited number of the subscribers in the private automatic exchange.

According to one feature of the invention, a special service trunk'is provided to which the lines of subscribers entitled to secret service, and the incoming trunk line, over which the secret servicefacilities are to be provided, may be connected under control of the subscribers entitled to the service.

According to another feature of the inVen tion, an incoming callover the trunk line is completed in'the regular manner by the attendant by means of acord circuit and, by the operation of a key at the subscribers station, both the trunk line and the subscribers line are disconnected from the jacks at the attendants cabnet and connected to the special service trunk. I

A stillfurther feature of the invention lies in the arrangement which prevents a second privileged subscriber from connecting his line to the special secret service trunk while a connection is established thereover.

The above and other features of the invention not specifically mentioned atthis time will be clearly understood from a perusal of the following description and explanation of the same when read in connection with the accompanying drawing comprising'one finger only, which shows by means of the usual schematic diagram sufficient apparatus at a private automatic exchange to'enable the invention to be understood. i

The trunk line comprising conductors 1 and 2 connects the private automatic exchange with a second exchange and terminates in the P. A. X. in thejack J at theattendants cabinet. The usual ring-up relay with its mechanical locking arrangement,

on this trunk line.

and the cut-off and busy relay 6 is provided The subscribers s'ubsta tions indicated as T1 and T2 are subscribers of the P. A. X. who are entitled to the secret service. The subscribers lines 44 and 45, and 46 and 47 are normally connected to the line-multiple jacksJ 1 and J 2"at the attend ants cabinet, and to the P. A. X. lineswitches and connector bank terminals over conductors 27, 28, and 29, and 37, 38, and 39, respec'tively. I

'A detailed description of the operation of the invention willnow' be given. For'this purpose, it will be assumed that the trunk l ne comprising conductors 1 and 2 has been seized in a distant oflice by an operator or by anautomatic switch having access there- 65 to; The ringing current projectedover the trunk line extends over armature 15 and its resting contact, condenser 9, Winding of r1ng-up relay 3, resting contact of armature 7 and said armature, resting contact of armature' 14 and said armature, to'the other trunk conductor 2 Relay 3 responds to the ringmg current and operates its armature 4 which 7 is thereupon mechanically locked up by means of the well-known interlocking arrangement indicated diagrannnatically at 5. The closing of armature 4 and'its working contact connects ground to the line lamp l0 and, through theresting contact of armature 8 and said armature to the busy lamp 11. These two lamps light up to inform the 0per- I ator that a call is Waiting on the trunk line accessible at the attendants cabinet over jack J. I

The attendant, upon noting the lighted condition of the 'line lamp 10, inserts the answering plug of a cord circuit into jack J. The cord circuits at the attendants cabinet may be of the well-known common battery type. J ack'springs 12 are closed, thereby connecting ground through the winding of relay 6 to battery. Relay 6 operates and at armature 7 and its resting contact, opens the circuit to the ring-up relay 3, and at the same time releases the mechanical locking ar- 95 rangement so that armature 4 of relay 3 restores tonormal and extinguishes line lamp I 10. At armature 8 and its resting contact, relay 6 opens the original circuit for the busy lamp 11 and at the Working contact of this 100 armature it connects ground directly to the lamp to maintain this lamp lighted to mark the trunk busy.

The attendant now converses with the party who has originated the call over the trunk line and finds out to whom he wishes to speak. It will be assumed that the calling party desires to talk with the subscriber at substation T1. Accordingly, the attendant inserts the calling plug of the cord into the line-multiple jack J1 associated with the line extending to substation T1. She then rings the subscriber at substation T1 in the usual manner and when the subscriber answers the talking connection is completed over jacks J and J1 and the cord circuit at the attendants cabinet.

In case-the calling man and the subscriber at substation Tl wishto eliminate all possibility of any one overhearing their CQI versation, the subscriber at substation T1 m0, mentarily operates the key K1. The closing of the contacts of this key completes a circuit from battery, upper winding of relay 1 20, contacts of key K1, conductor 48, winding of relay 13 to ground. Relays 13 and 20 operate in series in this circuit. At armature 21 and its working contact, relay 2 0 prepares a locking circuit for itself independent of the key K1. At armatures 22 and 23 and their resting contacts it disconnects the subscribers line from the line-multiple jack J1 at theattendants cabinet and from the subscribers lineswitch and connector bank normals, and

. at the working contacts of these armatures connects the subscribers line to the secret service trunk comprising conductors 1 2 and 43. At armature and its working contact it connects ground to conductor 27 to make the line of the stbscriber at substation T1 busy in the bank of connectors and to, ground the sleeve of jack J1 so that thelinewill test busy at the attendants cabinet, At armature 24 and its working contact relay 20 places its low 2 resistance lower winding in multiple with the high resistance upper winding to act as a shunt .to corresponding relays of other subscribers entitled to. this service, thereby preventing any other subscriber, such as. the one at substation T2, from connectinghis line to the secret service trunk.

Relay 13, in operating, at armatures 1 1 and 15 and their resting. contacts disconnectsithe incoming trunk line comprising conductorsl and 2 from the jack J1 atthe attendants cabinet, and at the working contacts of these armatures connects, the trunk line through condensers and 11 to the secret service trunk comprising conductors 42 and 43. When the subscribers fline comprising conductors 1 1. an 4:5 isconnected, to. the Secret service trunk line, relay16v operates. in a, circuit from ground,lower winding of relay 16, conductor 43, workingcontactot, armature22 a id se-i lerieat re .55 1 l i 4s' hr i eh the loop at substation T1, line conductor 45, armature 23 and its working contact, conductor 42, upper winding of relay 16, to battery. Relay 16 operates in this circuit and at armature 17 and its working contact connects ground to the busy lamp 11 to maintain this lamp lighted. At armature 18 and its working contact it completes the previously prepared locking circuit for relays 13 and 20. This locking circuit extends from ground, winding of relay 13, conductor l8, working contact of armature 21 and said armature, upper winding of relay 20 to battery, and in parallel thereto over armature 24 and its working contact, lower winding of relay 0 to battery, The key Kl at substation T1 may now be released. As long as the conversation continues over the secret service trunk, the trunk line comprising conductors land 2 will be made busy at the attendants cabinet since ground is maintained on the busy lamp 11 at armature 17 and its working contact. This busy condition will be maintained even though the at,- tendant withdraws the plugs of the cord circuit from jacks J and J1 when she learns that the connection is no longer completed over her cord circuit.

Should one of the other subscribers entitled to the secret service attempt to get in on the secret service trunk while the above-established conversation is going on, he is prevented from so doing by the low resistance lower winding of relay 20, which effectively shunts out all other relays such as 20 and 30. Assuming thatthe subscriber at substation T2 attempts to get in on the secret service trunk, he will operate his key K2, thereby completing a circuit from battery, upper winding of relay 30, contactsof keyeK2, conductor 48, winding of relay 13, to ground. However, the high resistance upper winding of relay 30 does not receive sufficient current to operate this relay since its winding is in multiple with the low resistance lower winding of relay 20. It is, therefore, seen that when one of the subscribers has connected his line to the secret; service trunk, none of the other subscribers entitled to the secret service can interfere.

The subscriber in the P. A. X.,' such as the subscriber at substation T1 in the aboveestablished connection, receives talking battery through thelwindings of relay 16; The subscriber in the distant office receives talking battery locally in the ofiice.

When the conversation has been complet ed, the subscriber at substation T1 replaces his receiver, thereby opening the loop circuit and allowing relay 16 to release. In releasin'g, relay 16 at armature'17 and itsworking contact disconnects. ground from the busy lamp 11 to inform the attendant that, thetrunk is again free. At armature 18and its work ing contact it opens the locking. circuit-of release. Relay 13 at armatures '14 and 15 again connects theincoming trunk-line conductors l and 2 to the'jackJ at the attendants cabinet. Relay 20, in releasing, at armatures 22 and 23 disconnects the subscribers line from the secret service trunk and againconnects the line to the jack J 1' at the attendants cabinet and over conductors 28 and 29 to the line switch in theP. A. K. At armature 21 and its working contact it opens a point in the looking circuit, at armature 24 and its working contact itagain opensa' point in the circuit of the lower winding of the relay, and at armature 25 and its working contact it disconnects ground from conductor 27 to remove the busy condition at the jack J1 and'in the banks of the connectors. All the apparatus used in the establishment of the original connection and over the secret service trunk has now been restored to normal.

The subscriber at substation T2 may connect his line to the secret service trunk by operating key K2 which brings about operations similar to those described above. In this case relay 30 operates in series with relay 13 to perform the switching operations.

Outgoing connections from the subscribers at substations such as T1 and T2 may be completed in any well known manner. -For example, a subscriber, in desiring to make a call over the trunk line comprising conductors 1 and 2, might call the attendant over the automatic switch train. The attendant would answer by means of her cord circuit and upon learning that a call is to be extended over the trunk line would complete the connection by means of her cord. In this case also the subscriber could obtain secret service, the operation of the key at the calling station cutting oil the subscribers line from the automatic switch train and connecting it to the secret service trunk, and also disconnecting the trunk line from the manual board and connecting it to the secret service trunk.

From the foregoing explanation, it is seen that the invention provides a simple and inexpensive method of giving secret service to a number of subscribers in a P. A. X. This is especially useful in a case where the P. A. X. is located in a manufacturing plant or similar establishment and the trunk line extends to a distant exchange or to another P. A. X. located in the main ofiices of the company. In this case, the president of the company might have his office in the main oflice building and the subscribers at sub-stations T1 and T2 at the P. A. X. might be vice-presidents or other high officials. In such a case, it would prove quite expensive to equip all of the cords at the attendants cabinet with secret service features or to provide other known systems of secret service since only two or possibly three of the lines in the P. A. X.

are to be given such service. The arrange ment might" also-be applied to, other systems and is not to beconsidered as limited to the particular arrangement shoWn.-. What is claimed is:

. 1.In" a telephonesystem, an incoming trunk lineaterminating in a manual board, a plurality of subscribers lines terminating in said board, some of saidlines being entitled to secret service, means at'said manual boardfor completing..Tconnections between said trunk: line and said subscribers lines,and :means controlled from. a line entitled to. said secretser-vice and to which a connection has been established for establishing a talking connectionbetweensaid line and said trunk line independent of said manual board. V

-2.- Ini a ftelephone system, an incoming trunk line terminating in anattendants cabi net, subscribers linesterminating in said at;- tendants cabinet, means for interconnecting said trnnk'line and one of said subscribers lines .toscompletea telephone connection, a secret. service trunk, and means controlled from the station on the connected line. for disconnecting :said line and said trunk line from. said attendants cabinetand'for connecting them to said secret service trunk;

3. In fa telephone system, an incoming trunk lineterminating in an attendants cabinet, subscribers lines also terminating in said attendants cabinet, means at saidattendants cabinet for interconnecting said trunk line other subscribers line to -said'secret service trunk.

' 4. In :a telephone system, an incoming trunk line terminating-in an attendants cabi- -net,- subscribers lines each terminating in a ack at said attendantsxcabinet and in an automatic switch, means at the "attendants cabinet for completing a connectionfrom said trunk-line toa: desired called line over the associated jack, a special trunk, a'n'd means controlled. fromthe called station for discon- .necting 'theincoming trunk-line andthe .c'alled line from said attendantscabinet and connecting themfto said special trunk.

5. In a telephone system, an incoming trunk line normally-terminating'in a jackat anattendants cabinet, subscribers lines each normally terminating in an automatic switch I I and in a jack at the attendants cabinet, means responslve to'an incoming call over said trunk line for signalling the attendant, means for completing the connection to'the desired sub- .scribers line over'the associatedline jack, -:a secret service trunk comprising two seca telephone connection, a key at each'subscribers station, a secret service trunk, means responsive to the operation ofthekey'at the staytion on the connected line for disconnecting said trunk line and said subscribers-line from said attendants cabinet and connecting them tosaid: secret service trunk, and means in said secret service trunk responsive to the connection'of said subscribers line thereto for maintaining. said connection independently of said key.

7. Ina telephonesystem, an incomingtrunk line terminating in: a manual board, subscribers lines terminating in said board, means for interconnecting said trunk line and one of said subscribers lines to establish'a telephone connection, a key at the station on the connected line, a talking trunk, a first and a second relay,means responsive tothe operation of said key for completing an energizing'circuit for said two relays inseries,

first-section of said talking trunk and for disconnecting'said trunk line from said man ual board and connecting it to the second section of said talking trunk, a battery feed relay in said firstsection, and means controlled by said relay for maintaining said connections until" said'subscribers line is released and for marking said trunk line busy at the manual board. c i c i In Witness whereof, I hereunto subscribe irgy name this25th day of February, A. D.

THOMAS F. cRooKER;

contacts on said first relay for disconnecting said trunk line' from' said manual board and connecting it to one end ofsaid talking trunk,

andcontacts on saidsecond'i'elay'for disconnecting. said subscribers linefrom'said manual board andcfor connecting it to the other end of said talking trunk. f

8. In a telephone system, a trunk lineter- I 'minating in a manualboard', subscribers lines terminating in said manual board, a secret service trunk, means controlled fromthe station on any one of said subscribers linesfor disconnecting such line and said trunk line from the-manual board and for-connecting them to said secret service trunk, means responsive to said last means for; busyin'g said line and'said trunk line at the manual: board, and means for preventing the connection of any other of said subscribers lines to said secret service trunk While said first'connection is maintained. V

9: In a telephone system, a trunk line terminating in a manual board, subscribers lines terminating. insaid board,cmeans for completing a telephone connection between said trunk lineand vone of said-subscribers lines,

'a' talking trunk comprising: tWo sections,

means'controlled from the station on thesconnectedline for disconnecting.- said line from the manual board and connecting it to the 

